The classic argument is simply someone who isn't a Roman Catholic.
Protestants don't believe in a Pope as the head of the church.
Protestants don't believe in a sinless perpetual virgin Mary.
Protestants don't believe Mary is a prayer intercessory or mediator.
Protestants don't believe in purgatory.
Protestants don't believe in indulgences.
Protestants maintain the bible alone is the written authroity of God. The one source of Christian faith or power to believe .
Roman Catholics follow their own law book oral traditions of dying mankind (CCC) Passed on from generation to generation .That they call apostolical succession. Which become false apostles false prophets that bring what they call Sacred Tradition of dying mankind .
They teach that both "I heard it through the father grape vine as a sacred tradition of dying mankind" and "all things writen in the law and prophets (sola scriptura) was the same source of faith.
Mentioning what they call sacred traditons first and the living word of God Sacred scripture that which follows
CCC 80 "Sacred Tradition and Sacred Scripture, then, are bound closely together, and communicate one with the other. For both of them, flowing out from the same divine well-spring, come together in some fashion to form one thing, and move towards the same goal."
When they tried to prove Paul was a false apostle that brings what some call sacred tradition .They shot themselves in the foot .
Believers miraculously can worship the one God of the fathers .Not a legion of fathers or patron saints as if our one Holy Father
Acts24:13-14;Neither can they prove the things whereof they now accuse me.;But this I confess unto thee, that after the way which they call heresy, so worship I the God of my fathers, believing all things which are written in the law and in the prophets:
In that way no man can serve two written teaching masters as one Lord Love one hate the other, hate one love the other .